It is desirable in many applications to provide a structure, such as a radome structure, which will permit the transmission of energy, in either direction therethrough, only over a selected frequency range. For example, such a structure may be used to transmit energy only at relatively low RF (radio frequency) frequencies while preventing transmission at high RF frequencies, the range of high frequency opaqueness being preferably extended over as broad a range of the spectrum as possible. Such structures are normally desired to be energy reflective over such non-transmission energy range as opposed to being absorptive of the energy involved. Such behavior is generally referred to as "low pass band" behavior since it can be considered analogous to electrical filter circuitry with similar properties.
It has been suggested in the past that to achieve low pass behavior such structures use electrically insulative substrate layers, or sheets, having metalized patterns, sometimes referred to as metalized patches, placed thereon normally in a regularized pattern having selected patch dimensions and spacings and having selected shapes for the particular applications in which they are to be used. For example, the metalized patches may be square or circular in shape or may be in the form of multiple patch "window frame" configurations each multiple patch, for example, containing four symmetrically arranged subpatches to form each of the window patch metalized regions.
One of the problems with such designs is that in many cases they do not provide sufficient coverage in the frequency domain for the desired reflective behavior and often tend to vary excessively in their behavior with both the angle of incidence and the polarization of the radiation impinging thereon.
It is desirable, therefore, to achieve low pass filter type operation for such energy transmitting structures which will provide sufficient suppression of energy transmission therethrough over a wide portion of the frequency spectrum and will produce the desired low pass filter operation over a wide range of incidence angles and for various polarizations of the impinging energy. Moreover it is desirable in some applications that the desired low pass behavior have its performance maximized utilizing only a single thin substrate layer rather than by using multiple layer as proposed in previously used structures, particularly for those applications in which the physical constraints thereof demand that the material thickness be kept to a minimum.